Here's why:

* Formation: Carbon dioxide (CO₂) from the atmosphere dissolves in water (H₂O), forming carbonic acid. This happens naturally in rainwater, lakes, rivers, and oceans.

* Abundance: CO₂ is a major component of the atmosphere, and water is abundant on the Earth's surface. This means carbonic acid is present in almost all natural water bodies.

* Impact: Carbonic acid plays a crucial role in weathering rocks, creating caves, and contributing to the acidity of oceans.

While other natural acids like humic acid and citric acid exist, they are not as widespread or significant as carbonic acid in terms of global impact.